The present invention relates to improved methods and apparatus for applying powder to workpieces. The methods and apparatus may be utilized to apply powder to many different types of workpieces. However, it is believed that the methods and apparatus may be particularly advantageous when utilized to apply powder coatings to can interiors and can lids. Powder coating materials for coating containers are more in demand now than in the past due to increasingly more stringent government regulations on solvent emissions which are associated with liquid coating materials conventionally used in coating containers. Powder coating materials produce zero solvent emissions.
A known apparatus for applying powder to workpieces is disclosed in U.S. Pat. No. 4,987,001 issued Jan. 22, 1991 and entitled "Method and Apparatus for Coating the Interior Surface of Hollow, Tubular Articles". The apparatus disclosed in this patent includes a spray gun which sprays electrostatically charged powder onto workpieces. A powder supply system is provided to supply powder to the spray gun.
Another apparatus for spraying powder onto workpieces is disclosed in an unexamined Japanese patent application having a Kokai Number of 60,752 published Mar. 15, 1991 and entitled "Electrostatic Spray Gun". The apparatus disclosed in this patent application engages the opening of a gasoline can with an inner wall element of a powder spray nozzle. An outer wall element of the powder spray nozzle is maintained in a spaced apart relationship with the gas can. A catch piece has an elastic body which seals against the gas can. Once the inner wall element of the nozzle and the elastic body on the catch piece have engaged the gas can, electrostatically charged powder is applied to the gas can in an annular band which extends around the opening.